DESCRIPTION (applicant?s abstract): Environmental factors, hormones, and the brain interact to produce complex social behaviors, including those important for reproduction. The goal of the present series of studies, submitted by a new investigator, is to elucidate basic relationships between hormones and brain areas regulating sexual arousal and those important for the expression of behaviors reflecting sexual arousal. Songbirds provide an excellent model system for understanding this relationship. Song learning, production, and perception are known to be regulated by a specific group of sex steroid binding nuclei, known as "the song system"; however, little is known about brain areas regulating the motivation to sing. During the breeding season, song in male starlings (Sturnus vulgaris) is observed prior to pair formation and copulation and likely reflects male sexual arousal. The medial preoptic area (POM) is known in other species to be critical for the expression of male sexual arousal, and lesions to this nucleus disrupt singing and other courtship behaviors in male starlings, suggesting that the POM might regulate the motivation to sing within breeding context. The present proposal consists of four studies designed to understand the relationship between brain areas devoted exclusively to male song and the POM: 1) An anterograde and retrograde neuroanatomical tract tracing study aimed to determine neuroanatomical connections between the song system and the POM, 2) a POM lesion study comparing the effects of POM lesions on song sung within and outside of the breeding season, 3) an implant study in which an aromatase inhibitor will be implanted directly into the POM of castrated, testosterone treated male starlings to determine whether aromatase activity in the POM is critical for song sung in the breeding season, and 4) an investigation of the expression of the immediate early gene products of c-Fos and ZENK to explore further POM regulation of song in response to male or female stimulus birds presented during or outside of the breeding season. This work will define the role of the POM in male song and sexual behavior, could add another dimension to the current understanding of the neuroendocrine regulation of male song, and will serve to link two currently separate fields of research (research on birdsong and research on male sexual motivation), steps that are necessary to elucidate how the brain regulates complex social behaviors. In addition, this research could lay the groundwork for future studies on the etiology of disorders related to sexual arousal.